This invention relates to internal combustion engines having combustion chambers within which fuel is combusted and exhaust systems through which products of combustion pass before entering the atmosphere. More specifically, the invention relates to engines, systems, and methods for control of exhaust flow in an engine exhaust system that contains high-pressure and low-pressure turbines of a two-stage turbocharger and an exhaust valve for selectively diverting the flow around one of the turbines.
A known electronic engine control system comprises a processor-based engine controller that processes data from various sources to develop control data for controlling certain functions of the engine. One function that is controlled in certain engines is exhaust back-pressure. The control system processes certain data useful in setting desired exhaust back-pressure, and then uses the result of that processing to set the extent to which an exhaust back-pressure control valve is open.
Certain diesel engines that power motor vehicles have turbochargers that are effective to improve certain aspects of engine operation and performance. One such turbocharger is a two-stage turbocharger that comprises high- and low-pressure turbines in series flow relationship in the exhaust system and an exhaust by-pass valve that is in parallel flow relationship to the high-pressure turbine and under the control of the engine control system. The engine control system processes various data to control the extent to which the exhaust by-pass valve shunts flow around the high-pressure turbine such that exhaust back-pressure and engine boost are regulated in a manner that achieves desired engine operation. Certain changes in input parameters affecting engine operation make it appropriate to change the extent to which the by-pass valve shunts exhaust gas flow around the high-pressure turbine to the low-pressure turbine.
Briefly, the present invention relates to improvements in control of exhaust gas flow in a turbocharged engine of the type described above.
General principles of the invention contemplate the use of various parameters such engine temperature and engine speed for control of the by-pass valve. More specific principles relate to specific implementations of fuel- and speed-scheduled gain strategies for closed-loop control of the by-pass valve.
Accordingly a generic aspect of the invention relates to an internal combustion engine comprising combustion chambers within which fuel is combusted and an exhaust system through which exhaust flow containing products of combustion is conveyed from the engine. The exhaust system contains first and second turbines of a multi-stage turbocharger and a valve for selectively by-passing the exhaust flow around one of the turbines. A control system comprising a processor for processing data develops data for controlling the extent to which the valve selectively by-passes the exhaust flow around the one turbine.
The processor comprises a control strategy a) for processing data values of various parameters to develop a data value representing a desired set-point of operation for the valve corresponding to a desired exhaust by-pass flow around the one turbine, b) for processing the desired set-point data value and a data value correlated with the actual set-point of operation of the valve to develop a set-point error data value for closed-loop control of the actual set-point, c) for selecting a data value of closed-loop gain from a schedule based on a data value of a parameter that characterizes an aspect of engine operation, d) for processing both the selected data value of closed-loop gain and the set-point error data value to create a data value for a closed-loop output, and e) for using the data value for the closed-loop output to create a data value for a final output for forcing the actual set-point to the desired set-point.
Another generic aspect relates to the system that has just been described.
Still another generic aspect relates to the method that is performed by the system just described.
The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows.